This invention relates to a catalytic system for polymerizing olefins, particularly propylene and comonomers. The present invention involves a novel supported catalyst containing titanium, a cocatalyst containing an organometallic compound, a process for producing the catalyst, and use of the catalytic system to polymerize olefins by the coordinate complex (Ziegler-Natta) method.
The coordinate complex approach to polymerizing olefins has been known for almost 30 years, and thousands of catalytic systems involving that approach have been disclosed. Nevertheless, the quest for higher catalytic activity coupled with higher stereospecificity of the polymer continues. The present invention realizes these twin goals.
Activity is normally measured by the grams of polyolefin produced per gram of catalyst containing titanium or other transition metal. The higher the activity is, the lower the amount of metallic ash and corrosive halide left in the polymer. If the activity is high enough, e.g., .gtoreq.10,000, then the de-ashing step in processing the final polyolefin can be omitted--an important improvement.
For olefins such as propylene which can form isotactic structures, the higher the isotactic index is (up to about 97 percent), the better the physical properties of the polymer are found to be. Isotactic polypropylene is more ordered, less soluble in halocarbons or hydrocarbons, and useful for its higher strength than the more soluble atactic form. Isotactic indices of 93 or higher are favored for commercial polypropylene.
The polmerization of olefins is described in numerous patents, journal articles, and books. U.S. Pat. No. 4,069,169 discloses a component prepared by milling magnesium chloride, ethyl benzoate, and titanium tetrachloride followed by treatment with TiCl.sub.4, optionally in the presence of a hydrocarbon solvent.
U.S. Pat. No. 4,143,223 discloses a similar process and product produced by milling magnesium chloride, ethyl benzoate, and phenol plus post-treatment with TiCl.sub.4.
U.S. Pat. No. 4,157,435 discloses yet another process involving the copulverization of magnesium chloride, polysiloxane, and ethyl benzoate in the presence of TiCl.sub.4 or a TiCl.sub.4 complex followed by reaction with TiCl.sub.4.
U.S. Pat. No. 4,290,915 discloses a solid titanium catalytic component comprising copulverized magnesium chloride, ethyl benzoate, and silicone oil post-treated with hot TiCl.sub.4, washed with a hydrocarbon, and partially dried so that 1 to about 10 percent by weight of the component of hydrocarbon remains.
U.S. Pat. No. 3,789,036 discloses a process for preparing elastomeric, olefinic copolymers employing a catalytic system containing a component prepared by contacting an anhydrous, activated Mg, Mn, or Ca dihalide with a halogenated titanium compound. The activation is indicated by replacement of the most intense X-ray diffraction lines by a broadened peak.
All five of the disclosures cited above are incorporated by reference into this application.